XUL - XML User Interface Language, pronounced "Zool" is a framework employed by Mozilla in it's applications, such as the Firefox web browser. It is based on XML while also making use of CSS and HTML features.
XUL is used in the context of Mozilla applications, which consist of components like buttons, labels and text boxes - "widgets". The rendering and handling of user actions within the widget are under the control of the widget itself, while the layout of the widgets and their interactions is specified in the XUL document.
XUL makes use of numerous other technologies, such as JavaScript - which can be used to program individual widgets, XBL - the eXtensible Bindings Language - used to define "bindings" for widgets, which also allows for event handlers, and adding new interface elements and properties.
Another technology which can be employed in the context of XUL is XPConnect and XPCOM. XPCOM ( Cross Platform Component Object Model ) is a framework for writing cross-platform, modular software components in native languages, such as C or C++. XPCOM components can be used form within C, C++, JavaScript, Python, Java and Perl. XPConnect enables such XPCOM objects to be accessed from JavaScript.
It is similar, in some aspects, to XIML since it also aims to provide a way of describing user interfaces, and is based on XML. But there are many differences, one of the most significant ones being that XIML has a broader scope, aiming for a generalization and standardization of UI elements and interactions, while XUL has a more practical perspective, providing a working solution at the expense of standardization, and having a narrower scope.
